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Could also create two Advanced Segments, one showing traffic only from Safari, the other showing all traffic except from Safari, then compare the metrics to see how the Safari traffic differs from that which is not Safari (assuming it does).

Hello, Now i'm not an expert in this area, but if you look in the GA iOS SDK I believe that their is a way to track entrances by "bookmarks" Please check this out https://developers.google.com/analytics/devguides/collection/ios/devguide#trackingModes they have the utm_soucre paramater that should be able to be set to bookmark.

nice article, thanks for getting back to me